Mock case II: fitting residuals shown in ϕ-Z_GC projection. Panel a shows the number density (logarithmic scale) of the mock data, panel b shows the predicted number density of the best-fitted model, and panel c shows the residual (relative to mock data). Panels a–c are restricted to 6<R<7.5 kpc. The subsequent rows show the same information but for selected successive bins in R.